The objectives of this research project are threefold: a) to understand the folding, mechanisms of action, and evolutionary relationships between the family of cytochromes c from bacterial and eukaryotic sources, and investigate the evolutionary development of the photosynthetic and respiratory electron transport chains of which they are a part; b) to learn the molecular basis for genetic control in the lactose systems by x-ray and chemical examination of repressor and the repressor-operator complex; and c) to solve the crystal structure of human erythrocyte glucose-6-phosphate dehydrogenase and understand the reason for the observed effects of point mutations on enzymatic function. Refinement of oxidized and reduced tuna cytochrome c structures is nearly complete, and the x-ray structure and amino acid sequence of Paracoccus cytochrome c550 are now in press. The Pseudomonas cytochrome c551 structure analysis is now at 4 A resolution, and data are being collected to higher resolution. All of these cytochromes have proven to be members of the same large evolutionary family, with the same central "cytochrome fold." Lac repressor now can be obtained in hundred milligram quantities, with 100% operator binding capacity. Small crystals of purified repressor have been obtained, so far only 0.04 mm in typical dimension, but with good extinction and visible facets. Synthetic operator made in this group (21-base-pairs) has been tested and shown to bind competitively with natural operator to repressor, and to be IPTG- sensitive. We plan to co-crystallize repressor and operator and solve the crystal structure of the complex, and also to carry out physico- chemical studies on synthetic operator and modified analogs. The G6PD project is at the stage of purification and microcrystallization, but an x-ray analysis is planned.